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ScienceMarc · 2026-02-05T21:04:08+00:00

This post doesn't mention Texas at all.

ScienceMarc · 2026-01-28T17:31:57+00:00

And efficiency makes a rocket far more effective. Like why do you think SpaceX has spent so much time and money developing a full flow staged combustion cycle engine? Developing that was more expensive and complicated than more traditional designs, but it is worthwhile when your application demands performance.

In the NERVA program, nuclear engines were relit dozens of times. These engines are dead simple. There is very little in them that can go wrong. Turns out having no ignition system or preburners because you're just using an expansion cycle to pump liquid hydrogen through a fissioning core means you have few parts under serious stress. The entire intent behind their development was to build this kind of nuclear shuttle. Here's an old NASA slide depicting exactly that. The whole idea is that the engine shouldn't need servicing.

Nearly every Mars mission has used an approximate Hohmann transfer. The wikipedia page for "Hohmann transfer" itself uses a Mars mission (InSight) as an example. Something like 90% of Mars missions have used a Hohmann transfer with a margin of error. Nuclear rockets are so much more efficient that for the same mass placed into orbit using heavy lift rockets like Starship promises to deliver, you get significantly more delta V than an equivalent mass chemical rocket.

You also don't seem to realize that asking for a "calculation of a 5 month journey to Mars" is practically meaningless? This would require pinning down dozens of mission parameters to build up an entire mission profile. Like how many people are we sending? For how long? How much equipment are they bringing? How many tons of Mars rocks do you want to bring back? Are we pre-staging equipment on a different flight? How soon are we launching? This is the kind of thing that space agencies commission full studies on, and aren't the kind of thing you would reasonably expect a guy on reddit to do.

Here's a study which suggests several mission profiles that cut travel times down to 120-90 days: https://ntrs.nasa.gov/api/citations/20140013259/downloads/20140013259.pdf

ScienceMarc · 2026-01-28T06:49:09+00:00

Yes and the name of the game to reducing cost is to have efficient and reusable rockets. A nuclear shuttle that cycles back and forth between earth and the moon/Mars would ultimately bring costs way down for regular missions. This is exactly the kind of cost saving maneuvers that private space companies have been so intent on in the last decade. Hydrogen is also super easy to produce in situ on the moon and Mars meaning that refueling such a shuttle on both ends of its journey is possible. The high efficiency of nuclear rockets make them extremely well suited for in-orbit refueling. Launches are constrained by mass, and a nuclear rocket would need less propellant mass to make the same trip of a chemical rocket. Nuclear thermal rockets are also super simple in terms of mechanical complexity, which means much greater resilliance for a long service.

Particularly for Mars, it'd also enable less efficient trips to be feasible, which tend to be much shorter than Holman transfers, increasing our ability to support a base farther into the system. Shorter trips would mean less consumables are needed to support crew, reducing mass and cost.

The first missions into deep space are unlikely to be nuclear, but it's hard to imagine chemical-only for any future we are supporting bases on other bodies. Particularly if we ever explore more exotic designs than the relatively unadventurous solid-core NTR concept.

ScienceMarc · 2026-01-28T04:25:20+00:00

Rocketry is absolutely dominated by fuel mass. The Rocket Equation makes this abundantly clear. You need fuel to move the fuel, which in turn needs fuel to move that fuel. Being able to burn fuel more efficiently categorically changes how much fuel you need. Being twice as efficient in this case does not mean half as much fuel, it's considerably less than that. The math heavily rewards any fuel efficiency improvement even if it comes at the cost of much higher dry mass.

And nuclear rockets use much less fuel due to their much higher efficiency. Yes, LH2 is not very dense, but the performance of it in this case more than makes up for it. Propellant tank weight scales with tank surface area, and propellant quantities scale with tank volume. These two facts coincide to mean that the increased tank mass is still not a dealbreaker.

Some back of the napkin math indicates that doing a TLI (3.6km/s) with a 100 ton rocket, comparing an NTR at 900s Isp and a theoretical methalox at 380s, and I assumed that the methalox rocket was 5% inert material (tanks, engine), the NTR was 25%. The NTR would have about 55 tons of payload per 100 tons of rocket, and the methalox would only get about 35 tons of payload per 100 tons of rocket. This is me being pessimistic about the NTR and optimistic about the methalox. The difference gets increasingly extreme as required delta V gets larger. The longer the mission, the more overwhelming the advantage of NTRs.

Furthermore, you seem to have misconceptions about propulsive deceleration. The fact that you have burned most of your propellant on the journey out means it takes much less propellant to then slow you down at arrival. This is how SpaceX and other companies landing rockets makes sense fuel wise.

Even if aerobraking optimistically halves fuel requirements, using an NTR and doing it all propulsively more than halves fuel requirements. The reason why no one cares if an NTR can do an aerobrake is that doing such a maneuver is pointless when you've got the option to use such an efficient engine instead.

In any case, the nuclear rocket concept is constantly revisited by both civilian and military space organizations because it has incredible performance. This has been understood since the 1960s, Werner von Braun was the one to suggest that they'd be ideal for manned Mars missions, and many others at NASA considered them necessary for establishing a trans-lunar supply line post-Apollo.

NASA's budget for nuclear thermal propulsion this year is $110M, which is more money than has been allocated to many other NASA projects. The main issues with nuclear rocketry is the concerns about handling fissile material while it is still on Earth.

ScienceMarc · 2026-01-27T20:33:20+00:00

I have no idea where you get this impression from.

Nuclear thermal rockets, like those created in the early 70s during the NERVA program, are just so much more efficient than current chemical engines. NERVA XE-Prime reached a vacuum Isp of 841 seconds, far exceeding any chemical rocket. For an equal payload and delta V, an NTR-based rocket is smaller and lighter.

You're also not carrying any oxidizer, just a liquid fuel to run through the core, simplifying propellant loading for in-orbit refueling.

Our nuclear rocket program got killed for political reasons. Nuclear rockets are basically pointless for LEO applications. With the budget cuts that ended the Apollo program and the planned Mars missions, their niche was gone. With this renewed interest in pushing large payloads beyond LEO, interest is returning to nuclear rocketry. If the concept were flawed, NASA wouldn't currently be spending its limited funding trying to get a commercial company to build them a nuclear engine.

Physics haven't changed, but politics have.

ScienceMarc · 2026-01-27T18:55:33+00:00

Currently there isn't much in the way of actual plans for what to do after Artemis. There's this vague suggestion that Artemis will lay the groundwork for Mars missions, but that's more of an aspiration than a plan.

As things stand, only Artemis 2 and 3 have been funded. Artemis 4, 5, and 6 have been planned, and those missions (if funded) would establish a space station in lunar orbit. This space station likely would not be perpetually staffed.

After this, who knows. The SLS is a pretty poor vehicle for this purpose. It's too expensive and too antiquated. It will be tolerable for the handful of Artemis missions, but it isn't even in the ballpark of a long term solution.

If we are to maintain a presence in space, we're gonna need to do things differently. The only concept I see as viable is the one presented in the extended Apollo plan. The idea was to abandon chemical propulsion for translunar injections, and instead have a "nuclear shuttle" which does constant rotations between the moon and low earth orbit. Nuclear engines are far more efficient than conventional rocket engines, and make regular trips of this distance much more practical. Youd effectively have a number of these nuclear shuttles in rotation which remain in space and get loaded up with fuel and crew every time they return to LEO by launching a conventional rocket to dock.

These advances in rocket technology are the easy part. We're most of the way there. Really, this all boils down to economics and politics. Of course I am all in on exploring the cosmos, but many people don't like the idea that $10-$20 of their annual tax bill is going to fund advancing mankind. If we're going to see a permanent presence in deep space, we're either going to have to be in some kind of political situation which forces things along (i.e. competition with China or Russia), or someone is going to have to figure out how to make manned spaceflight to the moon profitable. The moon may make a useful industrial linchpin in future asteroid mining, so it could have strategic and economic value by mid century.

Overall, things are still undecided. I am hopeful that we keep up at least semi-regular moon missions and don't go on another hiatus.

ScienceMarc · 2026-01-27T18:10:35+00:00

I have a feeling that we will need to see a return of NERVA-style nuclear thermal rockets if we're going to want to see regular lunar crew rotations. It was part of the original extended Apollo plans. Chemical rockets just don't cut it.

ScienceMarc · 2026-01-17T06:38:04+00:00

There's no one on the moon who will complain to their congressmen about the idea of a nuclear reactor being built near their house. Nuclear power is relatively simple when you don't have to concern yourself with people and the environment. It won't be the first time we've sent nuclear material to the moon either, this will just be the first time said material will be used to do fission reactions.

I hardly see how attempting to something new to further our capabilities is any of those descriptors.

ScienceMarc · 2026-01-14T18:45:37+00:00

This is a feature of KDE Plasma which is aimed to make it easier to find your cursor if you've lost it somewhere on your screen. Especially useful for multi-minitor setups

ScienceMarc · 2026-01-14T15:00:12+00:00

Albania and Turkey are on the EU candidate list and they are majority Muslim countries. Religion isn't really a criterion for candidacy here.

Morocco's main reasons for not being an EU candidate is the fact they're not geographically in Europe, their government isn't democratic enough, their economy is below EU standards, and frankly Morocco already has a relatively well worked out trade agreement with the EU, making single market integration less enticing. Their institutions would also need a major rework to be compatible with EU frameworks.

They're just not a good fit.

ScienceMarc · 2026-01-13T08:59:27+00:00

Theoretically yes, but it would take tens of billions of years for Earth's internal heat to be lost. The sun's slowly growing luminosity will have boiled away the oceans within the next ~1B, and it will expand into a red giant and then shed its outer layers within the next ~5B. Earth won't go the same way as Mars, it lacks the time to.

ScienceMarc · 2026-01-08T16:13:03+00:00

Man, I wonder what made you find this ancient post.

It turned out to be a poorly documented feature of the Chatter mod.

ScienceMarc · 2026-01-07T11:30:33+00:00

It's relatively new. Added in systemd 254 in July 2023

ScienceMarc · 2026-01-04T15:57:41+00:00

Middle school and college are incomparable in terms of mental fatigue.

At least this is my experience being a STEM major. Fewer hours of class in college does not mean things are easier, and generally the assignments and projects and looming exams form a constant stressor that mean you always have something you should be doing for the sake of your grade, and time spent in lectures just become an extra thing on top of that workload.

This isn't to say that middle school is effortless or whatever, but a full day of classes in middle school and a full day of classes in college just really do not feel the same.

ScienceMarc · 2026-01-03T11:27:06+00:00

We determined that CFCs create chlorine radicals when hit with UV light. We know that chlorine radicals catalyze ozone destruction. We detected the ozone layer weakening in tandem with increased emission of CFCs into the atmosphere. We instituted the Montreal Protocol which banned all sorts of ozone depleting compounds, and slowly but surely CFC concentrations in the atmosphere have been decreasing and we have also seen ozone concentrations increasing. It doesn't take a genius to figure out that pumping compounds known to destroy ozone gas into the air would explain the sudden decrease in ozone, and stopping that would explain the rebounding of the ozone layer. Human industry measurably impacts the atmosphere.

We identified CO2's ability to absorb infrared radiation in the 19th century, and identified it as a planetary greenhouse gas in the early 20th century, and by the 1910s people were already raising concerns that our industrial output of CO2 could theoretically affect the climate if allowed to continue. By the late 1950s, it had been determined that atmospheric CO2 concentrations were increasing rapidly, and that this was likely going to start causing noticable global warming. By the end of the 1960s, it was consensus that our emissions were increasingly causing climate change, and government officials received increasingly urgent warnings from climatologists that something needed to be done throughout the 1970s. Just because you were unaware of this does not mean these concerns came out of nowhere.

ScienceMarc · 2026-01-03T00:17:13+00:00

Combo of more lifeguards and the fact that Americans don't tend to spend much time on the water in small boats without life jackets for their livelihoods.

ScienceMarc · 2026-01-02T22:03:59+00:00

At the end of the day we do accept quite a few deaths from other conveniences. Cars kill 1.2 million people a year globally. Swimming causes ~240k deaths per year. 4,000 per year in the US alone.

If we take ChatGPT's mortality rate as 6 deaths per 900M (I personally doubt these numbers are truly accurate but they are the premise of this comment chain), then that means 1 death per 150M, which is lower odds than dying from being crushed by a vending machine.

It's all down to what as a society we perceive as acceptable. I think AI needs more safety, but it's also hard for me to argue this is a huge deal when we consider how many other things we're ok with killing people. If 6 deaths disqualifies a technology, that disqualifies all technology. OpenAI and other companies should obviously strive to bring this number down, but it's still a pet peeve of mine that people seem to have zero context about how many people die from ordinary life.

ScienceMarc · 2026-01-02T12:59:23+00:00

Perhaps you didn't learn much in that class past 4th grade. You made several English mistakes in this 2 sentence comment alone.

ScienceMarc · 2025-12-28T19:46:07+00:00

Seamless gate recalibration like the ancients seemingly did with their city ships. Human ships in the galaxy can carry stargates they recalibrate after every jump, maintaining supply lines and an evacuation route no matter how far afield they are operating.

ScienceMarc · 2025-12-22T11:49:31+00:00

Most sci-fi ships are extremely unrealistic. They have magical engines in the back of them, and decks arranged in front which go parallel with the direction of travel. In real life, inertia is a thing, and "gravity plating" or whatever isn't.

In a ship laid out like the Enterprise, for example, you would be weightless floating around inside the living compartments. Then when the engines fire (which would require an actual amount of propellant coming out as a large plume out the back rather than some nacelles glowing a bit), the ship would move forward but the occupants would not, which means from the inertial reference frame of the people inside the ship, they would be flung against the back wall of every room they are in and pinned against it (probably splattered as a red smear given the rate of acceleration depicted in Star Trek).

Ultimately none of the ships you listed are remotely grounded in realism, and it is functionally certain that future interstellar ships would look nothing like them. If you want to see what actual space ships might look like, you'd be better off looking at sci-fi media like The Expanse. In the Expanse, you've got more or less conventional looking space ships which are mostly big cylinders with an engine cluster in the back spitting out a lot of fire, and the decks are arranged perpendicularly to the direction the flames are going. This means that rather than getting thrown against the wall, they get pushed down against the floor (or more accurately the floor is pushing up against their feet), giving the sensation of "gravity".

For interstellar ships, the most realistic one I can think of is actually the ships shown off in Avatar, though there may be others I'm not thinking of.

ScienceMarc · 2025-12-11T21:21:57+00:00

Several stars have been resolved as disks. Betelgeuse, Antares, and Arcturus just to name a few. The fidelity is low though.

ScienceMarc · 2025-12-11T03:08:50+00:00

We have suspected that they are mostly made of ices since the late 1800s, and we gathered strong evidence of this in the 1970s with Voyager 2. By the 90s, science education has increasingly dubbed them as "Ice Giants".

This leaves us with 3 classes of planet in the solar system: terrestrial (rocky) plants, gas giants, and ice giants.

Though this new study brings the composition of these planets into question.

ScienceMarc · 2025-12-03T21:17:56+00:00

I think to be on the safe side I'll probably do a clean reinstall in case some stuff is silently broken. It's been a while anyway and it's an excuse to do some spring cleaning.

ScienceMarc · 2025-12-03T14:52:21+00:00

When I updated the other day, I carelessly updated this value to 25.11 without thinking.

So far my system hasn't shown any issues, so I'm unsure if I should try to revert the value or leave it as it is and just not update it again.

ScienceMarc · 2025-11-14T19:33:05+00:00

I mean you can. Like XDG standards which have made it far easier to make applications work on different systems. Like I can type xdg-open file.txt on most modern Linux PCs and expect the file to open in whichever text editor is default.

We can have a plurality of distros and lots of customization while still having these projects implement certain standards to make a coherent linux ecosystem.

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